1. Field of the Invention
The invention relates to a catalyst material for reducing the nitrogen oxides in flue gases in the presence of ammonia.
2. Description of the Prior Art
German patent application DE-AS No. 24 58 888 (equivalent to U.S. Pat. No. 4,085,193), discloses a catalyst material which aids in catalytically reducing nitrogen oxides in exhaust gases in the presence of ammonia into molecular nitrogen. Titanium oxide and vanadium oxide, along with a number of other additives, such as molybdenum, tungsten, nickel, and cobalt, are used as the catalytically effective combination. These substances that are catalytically effective in combination are obtained in the form of hydroxides or water-soluble salts solely by coprecipitation with titanium acid. They are subsequently dried and calcined. The nitrogen oxides in flue gases in the presence of ammonia can be reduced with this catalyst material. However, the full effectiveness of this catalyst material is attained only at relatively high flue gas temperatures.
Another catalyst material has been proposed for reducing the nitrogen oxides in flue gases (German Pat. No. 35 31 810.4, and its equivalent U.S. patent application Ser. No. 904,184 filed Sept. 5, 1986), in which the calcined titanium oxide is used in the form of octahedrite and is coated only on the surface with vanadium oxide and tungsten oxide. With this catalyst material, the catalytic activity can be shifted to lower flue gas temperatures. It has been found that the durability of the octahedrite modification of the titanium oxide is dependent not only on temperature but also on various pretreatment factors.